Composition and process for substitutionally plating zinciferous surfaces

ABSTRACT

An acidic substitutional plating bath for zinciferous surfaces, particularly zinciferous metal-plated steel sheet, with which sludge production and equipment corrosion are inhibited and which has an improved heavy metal ion deposition efficiency is provided by an aqueous composition that has a pH of 2 to 4.5 and that contains 1.5 to 40 g/L of at least one heavy metal ion selected from nickel, iron, and cobalt; 0.5 to 10 g/L of phosphate ions; 1 to 250 g/L of sulfate ion; and 1 to 20 g/L of organic acid.

TECHNICAL FIELD

The present invention relates to an acidic substitutional plating bathcomposition, also called a "bath" herein for brevity, for application tozinciferous surfaces, particularly to steel sheet plated withzinc-containing metal (hereinafter referred to as zinciferousmetal-plated steel sheet), and to processes for using such a compositionto treat metals. More specifically, the present invention relates to anacidic substitutional plating bath composition that can be continuouslyemployed for long periods of time while maintaining its initialperformance and that, upon contact with the surface of zinciferousmetal-plated steel sheet, forms thereon a heavy metal film thatcontributes to the formation of a paint undercoat that is very stronglyadherent for paint films. This acidic substitutional plating bathcomposition can also improve the black rust resistance of the unpaintedsheet.

As used herein, the term "zinciferous metal-plated steel sheet"encompasses steel sheet plated with zinc or a zinc alloy. Said zincalloys encompass, for example, zinc-aluminum alloys, zinc-nickel alloys,and zinc-iron alloys.

BACKGROUND ART

In order to increase the adherence of zinciferous metal-plated steelsheet to paint or other types of dryable films coated thereon, treatmentof zinciferous metal-plated steel sheet with an acidic aqueous solution(particularly aqueous phosphate solutions) is widely used in industry inorder to form a paint undercoat film on the sheet. Paint films laid downon such a phosphate film layer perform well when the treatment has beenmanaged so as to give appropriate film weights and crystal dimensions.Since these physical parameters must be adjusted into appropriateranges, it therefore becomes necessary to vary the conversion treatmentconditions as a function of the type of plating on the steel sheet andthe steel sheet line speed and to frequently remove the sludge that isgenerated in the treatment bath.

In the case of low-lead hot-dip galvanized steel sheet (with a leadcontent in the zinc plating layer reduced from that in conventionalhot-dip galvanized steel sheet), it has already been discovered thatcorrosion inhibition is obtained due to the absence of lead segregationat the grain boundaries of the crystals in the plating layer and at theinterface between the plating layer and alloy layer. Low-lead hot-dipgalvanized steel sheet is, as a consequence, widely used in variousindustrial sectors. However, unlike the conventional hot-dip galvanizedsteel sheet, low-lead hot-dip galvanized steel sheet resists crackingduring bending processes, with the result that shear stresses becomeconcentrated in the phosphate film positioned between the steel sheetand paint film. This produces cohesive failure in the phosphate film,which in turn causes facile delamination of the paint film.

In order to avoid the problems described above, application-typechromate treatments that include hexavalent chromium and trivalentchromium are in use as paint undercoat treatments in place of phosphatetreatments. The treatment bath composition in this type of process iseasily maintained and managed. Moreover, this type of process can easilyrespond to many different types of plating and to line speed variations,and the treatment effluent in this case poses few environmentalproblems. However, the paint adherence of these chromate films is not asgood as that of the phosphate films, and in particular delamination ofthe paint film occurs quite easily during strong flexural workinginvolving pressure contact.

In order to improve the paint adherence of such application-typechromate films, i.e., in order remediate the problem of faciledelamination, (1) Japanese Patent Publication Number Sho 43-12974[12,974/1968], (2) Japanese Patent Publication Number Sho 52-22618[22,618/1977], (3) Japanese Patent Publication Number Sho 52-43171[43,171/1977], and (4) Japanese Patent Application Laid Open [Kokai orUnexamined] Number Sho 61-69978 [69,978/1986]propose methods forimproving the paint adherence by preliminarily subjecting zinciferousmetal-plated steel sheet to heavy metal substitutional plating with Ni,Co, and/or Fe, and so forth, prior to the execution thereon of thechromating treatment.

Considering these previous methods, (1) Japanese Patent PublicationNumber Sho 43-12974 relates to a method in which zinciferousmetal-plated steel sheet is treated with a basic aqueous solution(pH≧11) containing Co²⁺, Fe²⁺, Fe³⁺, or Ni²⁺ prior to execution of achromate treatment on the sheet. However, large amounts of sludge areproduced in this method due to the accumulation of the zinc ion elutinginto the treatment bath with elapsed treatment time. This necessitates asludge removal step, which impairs the workability.

(2) Japanese Patent Publication Number Sho 52-22618 and (3) JapanesePatent Publication Number Sho 52-43171 relate to methods in whichgalvanized steel sheet is treated with an acidic solution (pH around1.5) that contains Ni²⁺, Co²⁺, Fe²⁺, and/or Fe³⁺ prior to execution of achromate treatment on the sheet. For the purpose of regulating the pH,the acidic substitutional plating baths disclosed in (2) Japanese PatentPublication Number Sho 52-22618 and (3) Japanese Patent PublicationNumber Sho 52-43171 contain an inorganic acid such as hydrochloric acid,sulfuric acid, hydrofluoric acid, or fluosilicic acid, or an organicacid such as citric acid, acetic acid, oxalic acid, and so forth. Thezinc ion eluted into the plating bath is present in dissolved formthrough the formation of a salt with the inorganic acids or throughcomplex formation with the organic acids. The pH in substitutionalplating baths of this type is readily increased by the increase in zincion concentration, which results in a decline in the substitutionalplating reactions. Due to this, large quantities of inorganic acid mustbe added in order to maintain the pH of the plating bath at the desiredvalues, and this facilitates corrosion of, for example, stainless steelplating bath tanks, pipes, and so forth. Therefore such baths are quitedifficult to implement on a practical basis without the use of astainless steel reactor and piping both coated with rubber lining or thelike. This use of corrosive acid, particularly a volatile one such ashydrochloric acid, also causes a deterioration in the workingenvironment.

Finally, (4) Japanese Patent Application Laid Open Number Sho 61-69978concerns a method in with low-lead hot-dip galvanized steel sheet istreated with an aqueous alkaline solution that contains Fe, Co, and/orNi or with an aqueous hydrochloric acid solution, aqueous sulfuric acidsolution, or aqueous phosphoric acid solution that contains Fe, Co,and/or Ni. In the case of the aqueous hydrochloric acid solution,aqueous sulfuric acid solution, and aqueous alkaline solution,deposition of these metals is impaired by the increase in Zn ion andincrease in pH that occur with elapsed treatment time. On the otherhand, in the case of phosphoric acid, it would appear that its pHbuffering capacity suppresses the increase in pH, and thatsubstitutional deposition of the Fe, Ni, and/or Co then proceedssmoothly. However, absolutely no explanation of this point can be foundin the specification of document (4).

At the same time, chromate treatments have also been applied tozinciferous metal-plated steel sheet for the purpose of improving thecorrosion resistance. While this type of treatment very effectivelyinhibits the development of white rust, black rust (also known asblackening) still occurs during storage and transport. A countermeasureto this problem of post-chromating black rust consists, for example, offlash treatment by Ni, Co, or Fe as disclosed in Japanese PatentPublication Number Hei 3-49982 [49,982/1991].

In the technology described in Japanese Patent Publication Number Hei3-49982, black rust inhibition is achieved by the pre-chromatingtreatment of zinciferous metal-plated steel sheet with a treatment baththat has a pH of 1 to 4 or 11 to 13.5 and that contains Ni²⁺ ion or Co²⁺ion. Even this method, however, suffers from a reduced workability dueto the production of sludge that occurs when the zinc ion concentrationbecomes elevated during the course of treatment.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Thus, the execution prior to chromating of a substitutional platingtreatment on the surface of galvanized steel sheet using Ni, Co, and/orFe, etc., in accordance with the prior art as described above can solvethe problem of a poor paint adherence while also accruing the benefit ofincreasing the black rust resistance of the unpainted sheet.Accordingly, the present invention seeks to introduce a very generallyapplicable acidic bath composition for the substitutional plating ofzinciferous metal-plated steel sheet that is almost free of equipmentcorrosion and that is capable of a very efficient deposition of heavymetal (e.g., Ni, Co, and/or Fe, etc.) on zinciferous metal-plated steelsheet, with no sludge production with elapsed treatment time, despitethe increased zinc ion concentrations in the substitutional platingbath.

SUMMARY OF THE INVENTION

In specific terms, the acidic substitutional plating bath composition ofthe present invention for application to zinciferous metal-plated steelsheet characteristically has a pH of 2.0 to 4.5 and contains 1.5 to 40g/L as metal atoms of at least one heavy metal ion selected from nickel,iron, and cobalt; 0.5 to 10 g/L of phosphate ions, including thestoichiometric equivalent as phosphate ions of any undissociatedphosphoric acid present in the solution and of all the anions other thanphosphate itself produced by any degree of dissociation of phosphoricacid; 1 to 250 g/L of sulfate ions; and 1 to 20 g/L of organic acid.

The inventors have discovered that when phosphoric acid with its high pHbuffering capacity is used in the acidic substitutional plating bath inplace of the aforesaid inorganic acids, the pH variations are relaxeddespite the increases in the zinc ion concentration, and the amount offree inorganic acid ion can therefore be restrained. This makes possiblethe preparation of an acidic substitutional plating bath that solves theproblem with prior acidic substitutional plating baths through itsalmost complete lack of corrosiveness for stainless steel containers andpiping.

In addition, the plating baths disclosed in the prior-art examplesreferenced above contain compounds of antimony, tin, and so forth, inorder to prevent a decline in the substitutional plating reactions atincreased levels of zinc ion. With the goal for the present invention ofbeing able to maintain the initial substitutional plating reactions forlong periods of time without the addition of such compounds, the presentinventors discovered that regulation of the pH to 2.0 to 4.5 andlimiting the quantities of etching-active components (phosphate ions,sulfate ions, and organic acid ions) in the treatment bath to withinparticular ranges avoids the accumulation of large quantities of zincion and makes possible use of the plating bath on a continuous basis.

The acidic substitutional plating bath in accordance with the presentinvention must contain the following components:

First, the bath must contain at least one heavy metal ion selected fromnickel, iron, and cobalt. These are advantageously supplied to theplating bath in the form of the corresponding sulfates, phosphates,carbonates, oxides, hydroxides, and organic acid salts. The use ofnitrate is undesirable because its presence can lead to the formation ofa phosphate film upon zinc dissolution. In addition, long-term use ofthe chloride runs the risk of chloride ion accumulation and corrosion ofthe plating equipment.

The plating bath should contain said heavy metal ion(s) at 1.5 to 40 g/Lcalculated as metal atoms. Metal deposition is inadequate at below 1.5g/L and a satisfactory effect is therefore not obtained. At above 40g/L, on the other hand, metal deposition is saturated and the economiclosses due to bath carry-out become large.

Orthophosphoric acid is preferably used as the source for the phosphateion used by the present invention. The content of phosphoric acid in theplating bath should be 0.5 to 10 g/L as phosphate ion. The use of lessthan 0.5 g/L will result in a sharp increase in bath pH, whichinfluences the component balance. The pH buffering activity issubstantially saturated at above 10 g/L, while the amount of zincetching is increased, with a corresponding decline in depositionefficiency.

Sulfate ions in the present invention are preferably supplied bysulfuric acid. Its content gradually increases because it isgenerated--by zinc ion capture--in correspondence to the increase inzinc ion. Accordingly, the sulfate ion concentration should bedetermined by the amount of zinc etching and the amount of plating bathcarry-out, but must generally fall in the range of 1 to 250 g/L. Captureof the eluted zinc ion is inadequate at below 1 g/L, while exceeding 250g/L is economically unattractive because the effect is saturated at suchlevels.

The organic acid used by the present invention comprises at least oneselection from glycolic acid, lactic acid, malic acid, tartaric acid,citric acid, gluconic acid, and ascorbic acid. Preferably, the organicacid is citric or malic acid. The organic acid concentration should be 1to 20 g/L. Both the ability to capture eluted zinc and the pH bufferingcapacity are inadequate when the organic acid concentration is less than1 g/L. On the other hand, the effect becomes saturated when the organicacid concentration exceeds 20 g/L, and these high concentrations alsoimpair the heavy metal deposition efficiency.

An acidic substitutional plating bath in accordance with the presentinvention containing the ingredients as described above should have a pHadjusted into the range of 2.0 to 4.5. The pH value may be maintained inthis range through the supplementary addition of hydrofluoric acid orfluosilicic acid to the plating bath. Zinc oxide or ammonia can be addedwhen the pH is too low. The reasons for the restriction to the pH rangeof 2.0 to 4.5 are as follows: a pH below 2 signifies an excessivecontent of inorganic acid, which results in too much zinc etching;equipment corrosion also becomes a risk at lower pH values; at pH valuesin excess of 4.5 the substitutional plating reactivity is impaired whenthe amount of eluted zinc ion has become increased.

Acidic substitutional plating may be run by bringing the surface of thezinciferous metal-plated steel sheet into contact with the acidicsubstitutional plating bath by spraying, immersion, coating, and soforth. Plating is thereby conducted to the desired degree, and isfollowed by a water wash and drying. The temperature of the plating bathshould be room temperature to 80° C., and a treatment time of less than1 minute will be sufficient. Insofar as concerns the amount of heavymetal deposition, 1 to 100 mg/m² can provide a desirable performance inthe case of paint undercoating treatments, while 0.3 to 20 mg/m² canprovide a desirable black rust prevention in the case of anticorrosionchromate treatments. The desired effects may not appear when the amountof heavy metal does not meet these lower limits, while exceeding theupper limits is economically unattractive because no additionalimprovement in performance is obtained above the upper limits. Simplydriving off the water is sufficient for drying, and the sheettemperature in drying will generally fall in the range of 50° C. to 100°C.

The substitutional plating bath in accordance with the present inventionmay be applied to the surface of pure zinc, hot-dip galvanization,hot-dip galvanization that contains aluminum or iron as alloyingcomponents, and steel sheet electroplated with zinc or zinciferousmetal. After this substitutional plating, the zinciferous metal-platedsteel sheet is typically subjected to an application-type chromatetreatment for the purpose of improving the corrosion resistance, andthis is followed by painting. The execution of the subject surfacetreatment imparts a microscopically etched texture to the surface of thezinciferous metal-plated steel sheet, which has an anchoring effect onthe paint film. But in addition, interactions (reciprocal activities)occur between the deposited heavy metal and the post-treatment chromatefilm, and this has the effect of adsorptively fixing the chromate filmon the plated metal surface. The result of these effects is animprovement in adherence between paint films and the underlyingzinciferous metal-plated steel sheet. On the other hand, in the case ofthe execution of a chromate treatment on the zinciferous metal-platedsteel sheet after this substitutional plating treatment, the depositedCo, Ni, or Fe functions as a barrier to oxidation reactions, which isthought to inhibit the growth of an oxide film (=black rusting) on thedirectly underlying plating layer.

The invention may be appreciated in greater detail through considerationof the working examples provided below. These examples are provided inorder to aid in using the invention, but in no way restrict theinvention.

EXAMPLES Examples 1 to 3 and Comparison Examples 1 to 4

In each of Examples 1 to 3 and Comparison Examples 1 to 3, the testsheets [as described in General Condition (1) below] weresubstitutionally plated using a treatment bath with the compositionreported in Table 1. The organic acid was citric acid in Examples 1-6and malic acid in Examples 7-12. The substitutionally plated test sheetsand test sheet without substitutional plating (Comparison Example 4)were then cleaned, dried, chromated, and painted in this sequence asdescribed in (3) through (6) below. The painted test sheets weresubsequently submitted to flexural testing and corrosion resistancetesting as described in (7) and (8) below. Table 2 reports the followingvalues: the substitutional plating conditions, the presence/absence ofsludge production and the amount of zinc ion in the bath for treatmentbath into which zinc ion has been dissolved by the continuous treatmentof test sheets, the amount of heavy metal deposition by substitutionalplating, and the results of flexural testing and corrosion resistancetesting on the painted sheet.

General Conditions for Examples 1-3 and Comparison Examples 1-4

(1) Test sheet: Hot-dip zinc-plated steel sheet, minimized spangle,unoiled; sheet thickness=0.35 mm, plating weight=90 g/m².

(2) Substitutional plating treatment: As reported in Table 1.

(3) Cleaning: Spray wash for 10 seconds with tap water.

(4) Drying: Drier used.

                                      TABLE 1                                     __________________________________________________________________________    Example ("E")                                                                 and Comparison                                                                         Treatment Composition Characteristics                                Example ("CE")                                                                         g/L in the Composition of:                                           Numbers  Zn Ni Fe Co PO.sub.4.sup.-3                                                                   SO.sub.4.sup.-2                                                                   OA Other                                                                             pH                                        __________________________________________________________________________    E 1.1    0  -- -- 2.0                                                                              1.5 4   1.5                                                                              --  2.4                                       E 1.2    25 -- -- 2.0                                                                              1.5 38  1.6                                                                              --  2.4                                       E 1.3    50 -- -- 2.1                                                                              1.6 79  1.6                                                                              --  2.5                                       E 2.1    5  30 -- -- 4.0 49  3.0                                                                              ZnO 3.5                                       E 2.2    25 30 -- -- 4.1 81  3.0                                                                              --  3.5                                       E 2.3    50 30 -- -- 4.0 122 2.9                                                                              --  3.5                                       E 3.1    2  -- 6.8                                                                              -- 2.2 5   9.1                                                                              0.5 F.sup.-                                                                       2.1                                       E 3.2    15 -- 6.7                                                                              -- 2.1 27  9.0                                                                              0.5 F.sup.-                                                                       2.2                                       E 3.3    30 -- 7.0                                                                              -- 2.3 48  9.1                                                                              0.5 F.sup.-                                                                       2.1                                       CE 1.1   0  -- -- 2.0                                                                              --  10  1.5                                                                              --  2.4                                       CE 1.2   5  -- -- 2.0                                                                              --  25  1.5                                                                              --  3.8                                       CE 1.3   10 -- -- 2.0                                                                              --  50  1.6                                                                              --  4.9                                       CE 2.1*  0  -- 3.7                                                                              2.4                                                                              --  --  -- --  13.2                                      CE 2.2*  5  -- 3.7                                                                              2.5                                                                              --  --  -- --  13.1                                      CE 2.3*  10 -- 2.8                                                                              1.6                                                                              --  --  -- --  13.1                                      CE 3.1** 0  5.9                                                                              -- -- 48  6.5 -- --  1.8                                       CE 3.2** 5  5.9                                                                              -- -- 48  7.7 -- --  2.0                                       CE 3.3** 8  5.0                                                                              -- -- 29  8.4 -- --  2.1                                       CE 4     No substitutional plating                                            __________________________________________________________________________     Notes for Table 1                                                             "OA" = Organic Acid. In Example 2.1, an amount of zinc oxide sufficient t     result in 5 g/L of zinc ions was added at the beginning.                      *Example 1 in Japanese Patent Publication Number Sho 4312974                  **Example 2 in Japanese Patent Application Laid Open Number Sho 6169978  

                  TABLE 2                                                         ______________________________________                                        Example                                                                       ("E")                                                                         and                                                                           Com-   Sludge                                                                 parison                                                                              Production                                                             Example                                                                              in the    Conditions of                                                ("CE") Treatment Treatment     AOM,                                           Numbers                                                                              Bath?     Type    °C.                                                                         Sec  mg/m.sup.2                                                                          FTR  CTR                             ______________________________________                                        E 1.1  no        spray   65    7   18    5    NA                              E 1.2  no        spray   65    7   18    5    NA                              E 1.3  no        spray   65    7   17    5    NA                              E 2.1  no        dip     50   10   22    5    NA                              E 2.2  no        dip     50   10   21    5    NA                              E 2.3  no        dip     50   10   20    5    NA                              E 3.1  no        dip     45    5   8     5    NA                              E 3.2  no        dip     45    5   7     4    NA                              E 3.3  no        dip     45    5   8     5    NA                              CE 1.1 no        spray   50   12   8     5    NA                              CE 1.2 no        spray   50   12   1.0   2    NA                              CE 1.3 yes       spray   50   12   0.2   1    NA                              CE 2.1 no        spray   70   30   35    5    9 F                             CE 2.2 no        spray   70   30   10    4    8 M                             CE 2.3 yes       spray   70   30   --    --   --                              CE 3.1 no        spray   50    8   11    4    NA                              CE 3.2 no        spray   50    8   0.5   1    7 M                             CE 3.3 yes       spray   50    8   --    --   --                              CE 4   none                --      1    NA                                    ______________________________________                                         Notes for Table 2                                                             "AOM" = addon mass of heavy metal achieved by the substitutional plating;     "FTR" = flexural test results for painted, treated sheets after a 2 T         bend;                                                                         "CTR" = corrosion resistance test results for painted, treated sheets;        "Sec" = seconds of treatment time; "NA" = no abnormalities.              

General Conditions Continued

(5) Chromate treatment: An application-type chromate bath (aqueousdispersion containing 4% Cr⁶⁺, 2% Cr³⁺, and 9% SiO₂) was roll coated soas to give a chromium add-on of 60 mg/m², followed by drying in a 150°C. hot-air drying oven at a maximum attained sheet temperature of 60° C.

(6) Painting: A back-surface alkyd paint was applied by bar coating soas to yield a dry paint film thickness of 6 micrometers. This wasfollowed by drying in a 300° C. hot-air drying oven at a maximumattained sheet temperature of 210° C.

(7) Flexural testing of the painted sheet: In accordance with "TestMethods for Colored Galvanized Steel Sheet" of JIS G 3312, a 2T bendingtest was run on each test sheet at 20° C. using 2 inside bending spacersheets. The extent of delamination after tape peeling was evaluated onthe following scale: 5: no abnormalities; 4: only cracking ordelaminated area less than 5%; 3: delaminated area from 5% to less than25%; 2: delaminated area from 25% to less than 50%; 1: delaminated areaat least 50%.

(8) Corrosion resistance testing of the painted sheet: A 70×150 mmcoupon was cut from each test sheet and subjected to the salt-spray teststipulated in JIS Z 2371 for 500 hours. Blistering on the surface of thepainted coupon was then evaluated according to the criteria of theAmerican Society for Testing and Materials (ASTM).

With reference to the results reported in Tables 1 and 2, due to the pHincrease in correspondence to the increase in eluted zinc ion inComparison Example 1 (substitution plating bath without phosphate ion),the amount of heavy metal deposition declined and the flexural adherenceof the painted sheet decreased as a result. In Comparison Examples 2 and3, sludge was produced by the increase in quantity of zinc ion elution.In Comparison Example 4 (no substitutional plating), the painted sheetevidenced a poor adherence. In contrast to these results, in Examples 1to 3 in accordance with the invention, no sludge was produced even atincreased quantities of eluted zinc ion and it was possible to maintainthe initial performance for long periods of time.

Examples 4 to 6 and Comparison Examples 5 to 8

In Examples 4 to 6 and Comparison Examples 5 and 6, test sheets asreported in (1) below were subjected to substitutional platingtreatments using the treatment bath compositions reported in Table 3.The substitutionally plated test sheets and test sheet withoutsubstitutional plating (Comparison Example 8) were then cleaned, dried,chromated, and painted in this sequence as described in (3) through (6)below. In Comparison Example 7 the test sheet was treated with zincphosphate and then painted. The painted test sheets were subsequentlysubmitted to flexural testing and edge creepage testing as described in(7) and (8) below. Table 4 reports the following values: thesubstitutional plating conditions, the presence/absence of sludgeproduction and the amount of zinc ion in the bath for treatment bathinto which zinc ion has been dissolved by the continuous treatment oftest sheet, the amount of heavy metal deposition by substitutionalplating, and the results of flexural testing and edge creepage testingon the painted sheet.

General Condition for Examples 4-6 and Comparison Examples 5-8

(1) Test sheet: Ultra-low-lead hot-dip zinc-plated steel sheet (Pbcontent in plating bath=0.003%), unoiled; sheet thickness=0.4 mm,plating mass=125 g/m².

(2) Substitutional plating or other treatment: See Table 3.

(3) Cleaning: Spray wash for 10 seconds with tap water.

(4) Drying: Drier used.

(5) Chromate treatment: An application-type chromate bath (aqueousdispersion containing 3% Cr⁶⁺, 2% Cr³⁺, 7% SiO.sub. 2, and 0.5% resin)was roll coated so as to give a chromium add-on of 70 mg/m², followed bydrying in a 150° C. hot-air drying oven at a maximum attained sheettemperature of 60° C.

(6) Painting: An epoxy primer was applied by bar coating so as to yielda dry paint film thickness of 5 micrometers followed by baking in a 300°C. hot-air drying oven at a maximum attained sheet temperature of 195°C. A polyester top coat was applied so as to yield a dry paint filmthickness of 12 micrometers, followed by baking in a 300° C. hot-airdrying oven at a maximum attained sheet temperature of 220° C.

                                      TABLE 3                                     __________________________________________________________________________    Example ("E")                                                                 and Comparison                                                                         Treatment Composition Characteristics                                Example ("CE")                                                                         g/L in the Composition of:                                           Numbers  Zn Ni Fe Co PO.sub.4.sup.-3                                                                   SO.sub.4.sup.-2                                                                   OA Other                                                                             pH                                        __________________________________________________________________________    E 4.1     0 4.5                                                                              -- 2.0                                                                              5.1 11  2.9                                                                              --  2.8                                       E 4.2    25 4.5                                                                              -- 2.1                                                                              5.2 43  2.8                                                                              --  2.9                                       E 4.3    50 4.6                                                                              -- 2.1                                                                              5.1 70  2.9                                                                              --  3.0                                       E 5.1     5 -- 35 -- 0.8 63  1.3                                                                              1.6 F.sup.-                                                                       2.4                                       E 5.2    50 -- 35 -- 0.8 140 1.4                                                                              1.6 F.sup.-                                                                       2.4                                       E 5.3    100                                                                              -- 35 -- 0.8 210 1.4                                                                              1.5 F.sup.-                                                                       2.4                                       E 6.1     0 9.9                                                                              -- -- 8.6 2   8  NH.sub.3                                                                          3.8                                       E 6.2    25 9.9                                                                              -- -- 8.7 38  8  --  3.9                                       E 6.3    50 10.0                                                                             -- -- 8.7 82  9  --  4.0                                       CE 5.1    0 4.5                                                                              -- 2.0                                                                              5.1 1.9 10 9.4 2.6                                                                       NO.sub.3.sup.-                                CE 5.2    5 4.5                                                                              -- 2.0                                                                              5.1 2.0 9  9.9 2.5                                                                       NO.sub.3.sup.-                                CE 6.1    0 -- 35 -- 11  60  10.0                                                                             1.6 F.sup.-                                                                       1.4                                       CE 6.2   50 -- 34 -- 11  63  9.9                                                                              1.6 F.sup.-                                                                       1.6                                       CE 6.3   100                                                                              -- 34 -- 12  68  10.1                                                                             1.7 F.sup.-                                                                       1.8                                       CE 7     Zinc phosphate conversion coating of 1 g/m.sup.2                     CE 8     No substitutional plating or other coating before                    __________________________________________________________________________             painting                                                              Note for Table 3                                                              "OA" = Organic Acid.                                                     

                  TABLE 4                                                         ______________________________________                                        Example                                                                       ("E")                                                                         and                                                                           Com-   Sludge                                                                 parison                                                                              Production                                                             Example                                                                              in the    Conditions of                                                ("CE") Treatment Treatment     AOM,       ECT                                 Numbers                                                                              Bath?     Type    °C.                                                                         Sec  mg/m.sup.2                                                                          FTR  mm                              ______________________________________                                        E 4.1  no        dip     55   10   35    5    5                               E 4.2  no        dip     55   10   33    5    6                               E 4.3  no        dip     55   10   33    5    5                               E 5.1  no        dip     75   5    65    5    5                               E 5.2  no        dip     75   5    65    5    5                               E 5.3  no        dip     75   5    64    5    5                               E 6.1  no        spray   60   8    29    5    6                               E 6.2  no        spray   60   8    28    5    6                               E 6.3  no        spray   60   8    29    4    7                               CE 5.1 no        dip     45   8    19    5    7                               CE 5.2 no        dip     45   8    15*   2    5                               CE 6.1 no        spray   50   10   24    5    6                               CE 6.2 no        spray   50   10   4     4    9                               CE 6.3 yes       spray   50   10   0.2   1    16                              CE 7   not applicable      --      1    5                                     CE 8   none                --      1    20                                    ______________________________________                                         Notes for Table 4                                                             "AOM" = addon mass of heavy metal achieved by the substitutional plating;     "Sec" = seconds of treatment time; "FTR" = flexural test results for          painted, treated sheets after a 2 T bend; "ECT" = edge creepage results       for painted, treated sheets.                                             

General Condition Continued

(7) Flexural testing of the painted sheet: In accordance with "TestMethods for Colored Galvanized Steel Sheet" of JIS G 3312, a 1T bendingtest was run on each test sheet at 20° C. using 1 inside bending spacersheet. The extent of delamination after tape peeling was evaluated onthe same scale as for Examples 1-3.

(8) Edge creepage test on the painted sheet: 70×150 mm coupons were cutfrom the test sheets in such a way that fins projected out at the topand bottom on both ends. After 1000 hours of salt-spray testing inaccordance with JIS Z 2371, the maximum creepage widths (mm) from theedges were measured on both sides. The average value is reported.

With reference to the results reported in Tables 3 and 4, the paintedsheet evidenced a poor adherence in Comparison Examples 5 and 7 in whicha zinc phosphate coating was formed on ultra-low-lead hot-dipzinc-plated steel sheet. In Comparison Example 6 (low pH), the increasein the amount of eluted zinc ion caused a corresponding decline insubstitutional deposition of the heavy metal as well as the productionof sludge. The flexural adherence of the painted sheet and the edgecreepage of the painted sheet were poor in Comparison Example 8 (nosubstitutional plating treatment). In contrast to these results, aphosphate film was not produced in Examples 4 to 6 of the invention evenin the face of zinc ion elution and it was possible to maintain theinitial performance for long periods of time.

Examples 7 to 9 and Comparison Examples 9 to 11

In Examples 7 to 9 and Comparison Examples 9 and 10, test sheets asreported in (1) below were subjected to substitutional platingtreatments using the treatment bath compositions reported in Table 5.The substitutionally plated test sheets and test sheet withoutsubstitutional plating (Comparison Example 11) were then degreased,cleaned, dried, chromated, and painted in this sequence as described in(2) through (9) below. The thus-treated test sheets were subsequentlysubmitted to adherence testing on the painted sheet and corrosionresistance testing on the painted sheet as described in (10) and (11)below. Table 6 reports the following values: the substitutional platingconditions, the presence/absence of sludge production and the amount ofzinc ion in the bath for treatment bath into

                                      TABLE 5                                     __________________________________________________________________________    Example ("E")                                                                 and Comparison                                                                         Treatment Composition Characteristics                                Example ("CE")                                                                         g/L in the Composition of:                                           Numbers  Zn Ni Fe Co PO.sub.4.sup.-3                                                                   SO.sub.4.sup.-2                                                                   OA Other                                                                             pH                                        __________________________________________________________________________    E 7.1     0 -- 1.0                                                                              1.4                                                                              2.9 19  4.9                                                                              --  3.0                                       E 7.2    25 -- 1.0                                                                              1.4                                                                              2.8 37  5.0                                                                              --  3.1                                       E 7.3    50 -- 0.9                                                                              1.4                                                                              2.8 73  5.0                                                                              --  3.0                                       E 8.1     0 3.1                                                                              -- -- 5.1  5  3.5                                                                              --  2.5                                       E 8.2    25 3.1                                                                              -- -- 5.0 32  3.5                                                                              --  2.5                                       E 8.3    50 3.2                                                                              -- -- 5.2 69  3.5                                                                              --  2.5                                       E 9.1     5 35 -- -- 4.7 64  2.1                                                                              1.8 F.sup.-                                                                       4.2                                       E 9.2    50 35 -- -- 4.6 101 2.0                                                                              1.8 F.sup.-                                                                       4.2                                       E 9.3    100                                                                              35 -- -- 4.5 145 2.0                                                                              1.7 F.sup.-                                                                       4.3                                       CE 9.1    0 -- 1.0                                                                              1.4                                                                              2.9 19  -- --  3.3                                       CE 9.2   10 -- 1.0                                                                              1.4                                                                              2.9 27  -- --  3.9                                       CE 9.3   25 -- 1.0                                                                              1.4                                                                              2.8 35  -- --  5.0                                       CE 10.1   0 -- 0.8                                                                              0.4                                                                              2.9 19  4  --  3.0                                       CE 10.2   5 -- 0.8                                                                              0.4                                                                              2.9 22  4  --  3.0                                       CE 11    No substitutional plating or other coating before                    __________________________________________________________________________             painting                                                              Note for Table 5                                                              "OA" = Organic Acid.                                                     

                                      TABLE 6                                     __________________________________________________________________________    Example ("E")                                                                         Sludge                                                                and Compar--                                                                          Production            Adherence                                       ison Example                                                                          In the                                                                              Conditions of   Test                                            ("CE")  Treatment                                                                           Treatment   AOM,                                                                              Results                                                                             mm                                        Numbers Bath? Type                                                                              °C.                                                                        Sec mg/m.sup.2                                                                        CT ET CR                                        __________________________________________________________________________    E 7.1   no    spray                                                                             70   8  25  4  4  0.2                                       E 7.2   no    spray                                                                             70   8  24  4  3  0.2                                       E 7.3   no    spray                                                                             70   8  24  4  4  0.2                                       E 8.1   no    dip 70  10  34  4  4  0.2                                       E 8.2   no    dip 70  10  36  4  4  0.2                                       E 8.3   no    dip 70  10  35  4  3  0.2                                       E 9.1   no    spray                                                                             60   5  14  4  4  0.5                                       E 9.2   no    spray                                                                             60   5  15  4  4  0.2                                       E 9.3   no    spray                                                                             60   5  15  4  4  0.5                                       CE 9.1  no    spray                                                                             60  10  17  4  3  0.2                                       CE 9.2  no    spray                                                                             60  10  7   4  3  0.2                                       CE 9.3  yes   spray                                                                             60  10  0.2 2  1  1.0                                       CE 10.1 no    spray                                                                             70  30  10  4  4  0.2                                       CE 10.2 no    spray                                                                             70  30  0.5 2  2  1.0                                       CE 11   none              --  1  1  1.5                                       __________________________________________________________________________     Notes for Table 6                                                             "Sec" = seconds of treatment time; "AOM" = addon mass of heavy metal          achieved by the substitutional plating; "CR" = corrosion resistance           results for painted, treated sheets; "CT" = checkerboard test; "ET" =         Erichsen test.                                                           

which zinc ion has been dissolved by the continuous treatment of testsheet, the amount of heavy metal deposition by substitutional plating,and the results of adherence testing and corrosion resistance testing onthe painted sheet.

General Conditions for Examples 7-9 and Comparison Examples 9-11

(1) Test sheet: Electrogalvanized steel sheet, oiled, sheetthickness=0.8 mm, plating mass=20 g/m².

(2) Degreasing: 30 second spray at 60° C. with a 2% aqueous solution ofan alkaline degreaser (PALKLIN™ N364S from Nihon Parkerizing Company,Limited).

(3) Cleaning: 10 second spray with tap water.

(4) Roll squeegee.

(5) Substitutional plating treatment: As reported in Table 5.

(6) Cleaning: 10 second spray with tap water.

(7) Drying: Drier used.

(8) Chromate treatment: An application-type chromate bath (aqueousdispersion containing 2% Cr⁶⁺ and 1% Cr³⁺) was roll coated so as to givea chromium add-on of 50 mg/m², followed by drying in a 250° C. hot-airdrying oven at a maximum attained sheet temperature of 150° C.

(9) Painting: A bakable melamine-alkyd paint was applied by bar coatingso as to yield a dry paint film thickness of 25 micrometers followed bybaking at a sheet temperature of 140° C. for 20 minutes.

(10) Adherence testing of the painted sheet: 1. Checkerboard test: Usinga cutter, a grid of 1 mm×1 mm squares was cut into the test sheet to thebasis metal; the extent of peeling of the paint film was evaluated afterpeeling with tape; 2. Erichsen test: A 6 mm extrusion was performed onthe test sheet using an Erichsen extruder; the extent of peeling of thepaint film was evaluated after peeling with tape; in the preceding twoitems, the paint film adherence was evaluated on the following fourlevel scale based on the extent of peeling of the paint film: 4:0% paintfilm peeling; 3: less than 10% paint film peeling; 2: from 10% to lessthan 30% paint film peeling; 1: at least 30% paint film peeling.

(11) Corrosion resistance of the painted sheet: A 70×150 mm coupon wascut from the test sheet, and a scribe line was made in the paint filmdown to the basis metal using a cutter. After 200 hours of salt-spraytesting, a tape peel was carried out, and the maximum single-side peelwidth (mm) from the scribe line was measured.

With reference to the results reported in Tables 5 and 6, as thequantity of eluted zinc ion increased in Comparison Example 9 (noaddition of organic acid), the amount of heavy metal deposition declineddue to the pH increase and sludge was also produced. In ComparisonExample 10 (low heavy metal ion concentration), the amount of heavymetal deposition declined as the amount of zinc ion increased, and theadherence by the painted sheet declined as a result. In ComparisonExample 11 (no substitutional plating treatment), the painted sheetevidenced a poor adherence and corrosion resistance. In contrast tothese results, in Examples 7 to 9 in accordance with the invention, theinitial performance was maintained in the long-term and the paintedsheet obtained had excellent properties.

Examples 10 to 12 and Comparison Examples 12 to 14

In Examples 10 to 12 and Comparison Examples 12 and 13, test sheets asreported in (1) below were subjected to substitutional platingtreatments using the treatment bath compositions reported in Table 7.The substitutionally plated test sheets and test sheet withoutsubstitutional plating (Comparison Example 14) were then cleaned, dried,and chromated in this sequence as described in (3) through (5) below.The thus-treated test sheets were subsequently submitted to acceleratedwhite rust testing and accelerated black rust testing as described in(6) and (7) below. Table 8 reports the following values: thesubstitutional plating conditions, the presence/absence of sludgeproduction and the amount of zinc ion in the bath for treatment bathinto which zinc ion has been dissolved by the continuous treatment oftest sheet, the amount of heavy metal deposition by substitutionalplating, and the results of accelerated white rust testing andaccelerated black rust testing.

General Conditions for Examples 10-12 and Comparison Examples 12-14

(1) Test sheets: Steel sheet plated with Zn/5% AI alloy, sheetthickness=0.7 mm, plating mass=90 g/m².

(2) Substitutional plating treatment: As reported in Table 7.

                                      TABLE 7                                     __________________________________________________________________________    Example ("E")                                                                 and Comparison                                                                         Treatment Composition Characteristics                                Example ("CE")                                                                         g/L in the Composition of:                                           Numbers  Zn Ni Fe Co PO.sub.4.sup.-3                                                                   SO.sub.4.sup.-2                                                                   OA Other                                                                             pH                                        __________________________________________________________________________    E 10.1    2 0.8                                                                              1.0                                                                              -- 1.0  3  1.2                                                                              ZnCO.sub.3                                                                        4.0                                       E 10.2   10 0.9                                                                              1.0                                                                              -- 0.9 15  1.2    4.1                                       E 10.3   25 0.8                                                                              1.0                                                                              -- 0.9 38  1.2    4.0                                       E 11.1    5 3.0                                                                              -- -- 4.0  9  3.0    3.2                                       E 11.2   25 3.0                                                                              -- -- 4.1 41  3.0    3.2                                       E 11.3   50 3.0                                                                              -- -- 4.0 75  2.9    3.2                                       E 12.1    2 -- -- 16 2.5  5  9.1                                                                              NH.sub.3                                                                          2.8                                       E 12.2   15 -- -- 16 2.6 27  9.0    2.7                                       E 12.3   30 -- -- 16 2.6 48  9.1    2.8                                       CE 12.1*  0 11 -- -- --  19  --     2.0                                       CE 12.2*  5 10 -- -- --  30  --     1.5                                       CE 12.3* 10 10 -- -- --  52  --     1.0                                       CE 13.1**                                                                               0 -- -- 11 --  17  15     13.2                                      CE 13.2**                                                                               5 -- -- 11 --  18  15     13.1                                      CE 13.3**                                                                              10 -- --  9 --  18  15     13.1                                      CE 14    No substitutional plating                                            __________________________________________________________________________     Notes for Table 1                                                             "OA" = Organic Acid.                                                          *Example 1(b) in Japanese Patent Publication Number Hei 349982                **Example 1(d) in Japanese Patent Publication Number Hei 349982          

                                      TABLE 8                                     __________________________________________________________________________             Sludge                                                               Example ("E")                                                                          Production                                                           and Comparison                                                                         In the                                                                              Conditions of                                                  Example ("CE")                                                                         Treatment                                                                           Treatment   AOM,                                               Numbers  Bath? Type                                                                              °C.                                                                        Sec mg/m.sup.2                                                                        RWR RBR                                        __________________________________________________________________________    E 10.1   no    spray                                                                             45  3   1.7 5   5                                          E 10.2   no    spray                                                                             45  3   1.6 5   5                                          E 10.3   no    spray                                                                             45  3   1.5 5   5                                          E 11.1   no    dip 60  5   2.5 5   5                                          E 11.2   no    dip 60  5   2.5 5   5                                          E 11.3   no    dip 60  5   2.4 5   5                                          E 12.1   no    dip 50  5   2.9 5   5                                          E 12.2   no    dip 50  5   2.8 5   5                                          E 12.3   no    dip 50  5   2.9 5   5                                          CE 12.1  no    dip 50  10  23.9                                                                              1   5                                          CE 12.2  no    dip 50  10  5.0 4   5                                          CE 12.3  no    dip 50  10  0.1 5   2                                          CE 13.1  no    dip 60  2   2.4 5   5                                          CE 13.2  no    dip 60  2   2.4 5   5                                          CE 13.3  yes   dip 60  2   2.2 5   5                                          CE 14    none              --  5   1                                          __________________________________________________________________________     Notes for Table 8                                                             "AOM" = addon mass of heavy metal achieved by the substitutional plating;     "RWR" = resistance to white rusting test results for painted, treated         sheets; "RBR" = resistance to black rusting test results for painted,         treated sheets; "Sec" = seconds of treatment time.                       

General Conditions Continued

(3) Cleaning: 10 second spray with tap water.

(4) Drying: Drier used.

(5) chromate treatment: An application-type chromate bath (4% Cr⁶⁺ and2% Cr³⁺)was roll coated so as to give a chromium add-on of 25 mg/m²,followed by drying in a 150° C. hot-air drying oven at a maximumattained sheet temperature of 60° C.

(6) Accelerated white rust testing: A 70×150 mm test coupon was cut fromthe test sheet and subjected to salt-spray testing in accordance withJIS Z 2371. The area of white rust development was visually rated after72 hours using the following criteria: 5: no white rust; 4: area ofwhite rust development less than 5%; 3: area of white rust developmentfrom 5% to less than 25%; 2: area of white rust development from 25% toless than 50%; 1: area of white rust development is at least 50%.

(7) Accelerated black rust testing: A multiple number of 70×150 mmcoupons were cut from the test sheet. Pairs were prepared by placing thetest surfaces of the coupons against one another, and these pairs werestacked. The entire assembly was wrapped with vinyl-coated paper, andthe four corners of the assembly were tightened down with bolts. A loadof 1 kgf/cm² was applied using a torque wrench. The assembly was heldfor 240 hours in a humidifying tester at 49° C. and 98% relativehumidity and subsequently withdrawn. Blackening of the overlaid regionswas then visually rated using the following criteria: 5: no blackening;4: very slight greying; 3: less than 25% blackening; 2: blackening from25% to less than 50%; 1: blackening at least 50%.

With reference to the results in Tables 7 and 8, there was a largeinitial heavy metal deposition in Comparison Example 12 (absence ofphosphate ion and organic acid) and the white rust resistance wastherefore poor. Subsequent to this, the heavy metal depositiondeclined--and the black rust resistance therefore declined--due to thedrop in pH as the eluted zinc ion increased. In Comparison Example 13,sludge was produced by the increase in quantity of eluted zinc ion. Theblack rust resistance was poor in Comparison Example 14 (nosubstitutional plating treatment). In contrast to this, in Examples 10to 12 in accordance with the invention, sludge production did not occurdespite the increase in amount of eluted zinc ion and it was possible tomaintain the initial performance for the long-term.

Benefits of the Invention

In application as a paint undercoating treatment, the acidicsubstitutional plating bath composition of the invention for zinciferousmetal-plated steel sheet imparts an excellent adherence and corrosionresistance to the painted sheet. In application as an undercoatingtreatment for chromating, this composition yields an excellent blackrust resistance. Moreover, the acidic substitutional plating bathcomposition of the invention retains its initial performance for longperiods of time and can therefore be used on a continuous basis.Finally, it is almost completely free of corrosiveness for equipment. Asa result of these attributes, the invention composition has substantialindustrial usefulness.

The invention claimed is:
 1. An aqueous substitutional plating bathcomposition having a pH of 2.0 to 4.5 and containing water and:(A) from1.5 to 40 g/L as metal atom of heavy metal ions selected from the groupconsisting of nickel, iron, cobalt, and mixtures of any two or morethereof; (B) from 0.5 to 10 g/L of phosphate ions; (C) from 1 to 250 g/Lof sulfate ions; and (D) from 1 to 20 g/L of organic acid.
 2. An aqueouscomposition in accordance with claim 1 in which the organic acid isselected from the group consisting of glycolic acid, lactic acid, malicacid, tartaric acid, citric acid, gluconic acid, ascorbic acid, andmixtures of any two or more thereof.
 3. An aqueous composition inaccordance with claim 2 comprising at least one of hydrofluoric acid,fluosilicic acid, zinc oxide, or ammonia.
 4. An aqueous composition inaccordance with claim 1 comprising at least one of hydrofluoric acid,fluosilicic acid, zinc oxide, or ammonia.
 5. A process comprising stepsof contacting a zinciferous surface with a composition according toclaim 4 for a time sufficient to deposit on the zinciferous surface atleast 0.3 mg of heavy metal per square meter of zinciferous surfacecontacted, removing the zinciferous surface from contact with theaqueous composition according to claim 4, washing the coating of heavymetal on the zinciferous surface with water, and drying the zinciferoussurface.
 6. A process according to claim 5, wherein the amount of heavymetal deposited on the zinciferous surface is from 1 to 100 mg/m² andthe dried zinciferous surface is subsequently painted.
 7. A processaccording to claim 5, wherein the amount of heavy metal deposited on thezinciferous surface is from 0.3 to 20 mg/m², and the dried zinciferoussurface is subsequently subjected to an anticorrosion chromatetreatment.
 8. A process according to claim 7, wherein the zinciferoussurface is that of zinciferous metal plated steel sheet.
 9. A processaccording to claim 5, wherein the zinciferous surface is that ofzinciferous metal plated steel sheet.
 10. A process comprising steps ofcontacting a zinciferous surface with a composition according to claim 3for a time sufficient to deposit on the zinciferous surface at least 0.3mg of heavy metal per square meter of zinciferous surface contacted,removing the zinciferous surface from contact with the aqueouscomposition according to claim 3, washing the coating of heavy metal onthe zinciferous suffice with water, and drying the zinciferous surface.11. A process according to claim 11, wherein the amount of heavy metaldeposited on the zincifirous surface is from 1 to 100 mg/m² and thedried zinciferous surface is subsequently painted.
 12. A processaccording to claim 11, wherein the amount of heavy metal deposited onthe zinciferous surface is from 0.3 to 20 mg/m², and the driedzinciferous surface is subsequently subjected to an anticorrosionchromate treatment.
 13. A process according to claim 12, wherein thezinciferous surface is that of zinciferous metal plated steel sheet. 14.A process comprising steps of contacting a zinciferous surface with acomposition according to claim 2 for a time sufficient to deposit on thezinciferous surface at least 0.3 mg of heavy metal per square meter ofzinciferous surface contacted, removing the zinciferous surface fromcontact with the aqueous composition according to claim 2, washing thecoating of heavy metal on the zinciferous surface with water, and dryingthe zinciferous surface.
 15. A process according to claim 14, whereinthe amount of heavy metal deposited on the zinciferous surface is from 1to 100 mg/m² and the dried zinciferous surface is subsequently painted.16. A process according to claim 15, wherein the amount of heavy metaldeposited on the zinciferous surface is from 0.3 to 20 mg/m² and thedried zinciferous surface is subsequently subjected to an anticorrosionchromate treatment.
 17. A process according to claim 16, wherein thezinciferous surface is that of zinciferous metal plated steel sheet. 18.A process comprising steps of contacting a zinciferous surface with acomposition according to claim 1 for a time sufficient to deposit on thezinciferous surface at least 0.3 mg of heavy metal per square meter ofzinciferous surface contacted, removing the zinciferous surface fromcontact with the aqueous composition according to claim 1, washing thecoating of heavy metal on the zinciferous surface with water, and dryingthe zinciferous surface.
 19. A process according to claim 18, whereinthe amount of heavy metal deposited on the zinciferous surface is tom 1to 100 mg/m² and the dried zinciferous surface is subsequently painted.20. A process according to claim 19, wherein the amount of heavy metaldeposited on the zinciferous surface is from 0.3 to 20 mg/m², the driedzinciferous surface is subsequently subjected to an anticorrosionchromate treatment, and the zinciferous surface is that of zinciferousmetal plated steel sheet.